1. Field of the Invention
The present invention relates to a broadband wireless access system, and more particularly, to a method of efficiently updating system information of a base station in a relay station and an apparatus for performing the method.
2. Discussion of the Related Art
It is expected that a relay station (RS) will widely be used in a wireless communication system for next generation. Hereinafter, the relay station (RS) will be described in brief.
A standardization project of a new title called multi-hop relay is currently in progress in IEEE (Institute of Electrical and Electronics Engineers) 802.16 of 2006 since publications of the standard IEEE 802.16-2004 based on fixed subscriber mobile stations and the standard IEEE 802.16e-2005 for providing mobility of subscriber mobile stations.
This standardization project handled by a task group j (IEEE 802.16j) within the IEEE 802.16 has started to discuss usage model, related terminologies, and technical requirements in the second meeting on July of 2006 after the first formal meeting on May of 2006. Hereinafter, the IEEE 802.16 task group j will be abbreviated as “802.16j”.
The concept of the relay station which will be described later can be used substantially the same as a relay station considered by a 3GPP LTE-A system. Also, a relay station that performs same or similar functions in other various wireless access systems can be used similarly to the relay station described in the present invention.
Project authorization request (PAR) of 802.16j is intended for coverage extension and throughput enhancement as standardization tasks which will be performed.
The relay station can be divided into two types of relay stations, i.e., a transparent relay station and a non-transparent relay station. According to the transparent relay station, all operations and functions are performed within the relay station, and a mobile station is managed by the relay station. On the other hand, according to the non-transparent relay station, all operations and functions are performed between a macro base station and a mobile station. In this case, the non-transparent relay station serves to perform its relay function through the macro base station between the macro base station and the mobile station.
The mobile station regards the transparent relay station and the non-transparent relay station as one macro base station without identification of the transparent relay station and the non-transparent relay station. In this case, although there is no change in operations, the mobile station may classify the relay station from the macro base station.
A network that includes a relay station includes a base station (BS), a relay station (RS), and a mobile station (MS). The mobile station can receive a radio signal even outside a cell zone of the base station through the relay station. Also, a path of high quality having an adaptive modulation and coding (AMC) scheme of high level can be set through the relay station for the mobile station within the cell zone of the base station. Accordingly, a user can obtain an advantage of system throughput enhancement by using the same radio resource.
The standard to be made by the 802.16j project has predetermined requirements. For example, the mobile station implemented based on the existing 802.16-2004 and 802.16e-2005 should perform communication with the relay station without any additional function. Accordingly, an application range of the relay station can be limited to the existing system in such a way to add some function for controlling the relay station to the relay station and the existing base station. It is expected that the standard for the relay station will be a core factor of the standardization.
The relay station can be regarded as a subscriber mobile station that performs operations of a physical layer and a media access control (MAC) layer. Also, the relay station is mainly controlled by the base station but may have a predetermined control function if necessary. As usage models currently in discussion, in addition to a fixed relay station, various types of relay stations are considered. Examples of the relay stations include a mobile relay station for temporarily providing a service to a specific zone and a relay station that can be built in cars or subways.
Main technical issues which will be discussed later can be described as follows:
1) a procedure for identifying a relay station existing in a base station and acquiring and maintaining information on topology with the relay station;
2) definition of a physical transport frame structure between a mobile station and a relay station, which have backward compatibility with the existing IEEE 802.16 system;
3) a signal procedure for providing mobility between relay stations or between a relay station and a base station; and
4) a network entry procedure of a relay station to a base station and an entry procedure of a mobile station through a relay station.
The relay station performs data exchange with both the mobile station and the base station. However, since the relay station is synchronized with the base station, the relay station and the base station broadcast system information at the same time. Accordingly, the relay station broadcasts its system information in accordance with a transmission mode at the time when the base station broadcasts system information. In this case, a problem occurs in that the relay station fails to receive system information of the base station. Also, as described above, the relay station has an interval for receiving data from the base station. In this respect, a method for reporting the interval to the mobile station and a subordinate relay station will be required.